Essential Formulas Reference

Quick reference for the most important electrical formulas on the Master Electrician exam.

Exam Tip

The exam is open book. You do not need to memorize every formula, but you do need to know where to find them quickly. Practice using the NEC tables and Chapter 9 until you can locate answers in under 3 minutes.

Ohm's Law

The foundation of all electrical calculations.

Voltage

V = I × R

V = Volts, I = Amps, R = Ohms

Example: 10A × 12Ω = 120V

Current

I = V / R

I = Amps, V = Volts, R = Ohms

Example: 120V / 12Ω = 10A

Resistance

R = V / I

R = Ohms, V = Volts, I = Amps

Example: 120V / 10A = 12Ω